It is known that a single Microsoft Exchange account is not sending more than 10k emails per day.
It is also know that once activated – Microsoft 365 groups ownerless policy will be sending notifications for all groups in scope to specified number of group members within 24 hours.
The question is: what if there are more than 10,000 notifications to send (e.g. 4,000 ownerless groups and the policy is configured to send notification to 3 members per group – that gives us 12,000 notifications to send)? Would the policy send 10k notifications and the rest 2k notifications the next day?
I’m conducting an experiment. I created 10k groups in my lab tenant with one owner and 3 random members. Then I configured a policy that is sending notification to a 3 most active members (in this case – random members). And then I made all these groups ownerless by deleting the single owner Id from Azure AD (Microsoft Entra).
Here is what I got from users perspective:
| user | user groups number | got messages day 1 | got messages day 2 | got messages total |
| 1 Roger | 5012 | 1374 | ||
| 2 Dick | 5039 | 1349 | ||
| 3 Bob | 5108 | 3412 | ||
| 4 Bapu | 4908 | 1376 | ||
| 5 Stas | 4996 | 1437 | ||
| 6 David | 4959 | 1377 | ||
| total | 10325 |
Here is what audit log says:
Events “OwnerlessGroupNotified” day 1: 4949
Events “OwnerlessGroupNotified” day 2: 95
Events “OwnerlessGroupNotified” total: 5044
Each event details says 3 members were notified.
It seems like groups are selected by policy in random order.
Massive E-mails sending was started 43 minutes after midnight UTC
“OwnerlessGroupNotified” were logged at the rate of
1925 events during 1-st hour,
2029 events during 2-nd hour,
785 events during 3-rd hour,
176 events during 4-th hour,
26 events during 5-24 th hour,
95 events during next 25-48 hours
so max rate was one event every 3 seconds in the beginning (or 1 e-mail per second) …
TBC…
